Output performance of internal combustion engines may vary significantly depending on the setting of various engine operating parameters, such as air-fuel ratio, spark timing, etc. In one particular example, spark timing, and more specifically settings for minimum timing for best torque (MBT), may affect vehicle fuel economy.
Typically, MBT spark timing is determined based on the results obtained from engine mapping. However, part variation and operating condition variations, even when extensively mapped, may still cause the spark to be set at a value providing less torque than another value closer to the actual MBT timing.
One approach to provide a feedback to control output torque and thereby address engine mapping errors is provided in U.S. Pat. No. 7,213,573. This example provides a system and associated subsystems that use a detected ionization signal to, among other things, control MBT timing.
However, the inventors herein have recognized a number of potential disadvantages with such an approach. As one example, the ionization current measuring circuit in the combustion chamber may degrade unpredictably due to part variation and differences in wear characteristics over time. Wear characteristics may be particularly difficult to predict for components located in harsh environments such as combustion chambers.
Thus, in one approach, a method is provided that includes adjusting the spark timing of an internal combustion engine configured to power a vehicle toward peak torque based on an output of a longitudinal acceleration sensor configured to sense a longitudinal acceleration of the vehicle. In this way, it may be possible to reduce reliance on sensors in harsh environments, and thereby reduce the uncertainties associated with component variation, and component aging. However, it should be appreciated that such an approach may also be combined with feedback from other sensors, such as an ionization sensor located in the combustion chamber, for example.
In one particular aspect, the spark timing may be adjusted during a steady state of the vehicle while the vehicle is in operation on a driving surface. The adjustment may be made on-line (in-vehicle) in real-time without, or in addition to, engine mapping data. Another aspect may thus provide measurement and feedback adaptation, which can form a closed-loop control. The adaptation and closed-loop control may increase the robustness against piece variations, aging and other disturbances, and also may enhance fuel efficiency and performance for individual engines by allowing individual compensation. Another aspect may make automated calibration possible with initial calibration, and refinement adaptation may also be possible to significantly enhance customer observed fuel economy.